As the use of public and private clouds becomes increasingly widespread, it is not uncommon for cloud infrastructure to include multi-site storage system arrangements. In such arrangements, a multi-site storage system may be distributed over multiple geographically-dispersed locations. A more particular example of a multi-site storage system is a virtual metro cluster, in which the sites may be within different regions of a metropolitan area or other geographic area and interconnected to communicate with one another via a wide area network (WAN). The different sites may correspond, for example, to different data centers of a business or other enterprise.
In conventional arrangements, each of the sites of the multi-site system may replicate file systems associated with the other sites, so as provide file system recovery capability in the event of failure of one or more of the sites. The remote site file systems that are replicated at the given site are also referred to as mirror file systems. However, in these conventional arrangements, the primary file system of a given site is typically mounted as a read-write file system but the file systems of the remote sites that are replicated as mirror file systems at the given site are typically mounted as read-only file systems.
Such arrangements are used because each primary file system of the multi-site storage system will generally include both cache and disk storage resources, and data written to a file system is held in cache for a certain period of time before it is sent to disk. Accordingly, as the replication of remote file systems generally involves replicating only the disk rather than both the disk and the cache, the conventional arrangements are unable to ensure consistent states between the replicated file system and its corresponding primary file system unless the replicated file system is mounted as a read-only file system.
The above-noted conventional arrangements are therefore unable to provide active-active data access in both primary and replicated file systems, where “active-active” indicates that both primary and replicated file systems of a given site are mounted as read-write file systems. Instead, as indicated previously such multi-site systems are typically configured to utilize “active-passive” data access, in which the primary file system is mounted as a read-write file system but the replicated file system is mounted as a read-only file system.
This represents a significant drawback of conventional practice, in that the file system recovery time after a failure in one of the sites can be unduly long when using an active-passive data access arrangement in a multi-site storage system.